The present invention generally relates to the processing of hydrocarbon compositions for the production of desired organic fractions, and more particularly to a hydrocarbon cracking method which is characterized by a high degree of efficiency, simplicity, insensitivity to contaminants, and versatility.
The processing of hydrocarbon compositions to manufacture lower molecular weight/lower boiling point organic products is commonly known as "cracking". Hydrocarbon cracking processes are widely used in many different technical fields, with particular importance in the petroleum processing industry. In addition, the cracking of hydrocarbon materials is useful in the production of specialty organic chemicals from long-chain (high molecular weight) organic precursor molecules. Regarding the petroleum industry, crude oil contains many valuable hydrocarbon compositions and is a very complex material. As stated in The Chemistry of Petroleum Hydrocarbons, Ch. 4, pp. 49-62, Benjamin T. Brooks (ed.), Reinhold Publishing Corp., New York (1954) [which is incorporated herein by reference], most crude oil compositions contain 83-87% by weight carbon, 11-14% by weight hydrogen, and 2-3% by weight elemental oxygen, nitrogen, and sulfur. Crude oil may also contain a variety of trace metals, including but not limited to nickel and vanadium.
Heavy and light crude oil compositions are very complex and typically include dozens of relatively large, high molecular weight C.sub.5 -C.sub.40 alkanes, C.sub.5 -C.sub.11 cycloalkanes, and C.sub.6 -C.sub.13 aromatic hydrocarbons. Exemplary alkanes which are present in typical supplies of crude oil include but are not limited to n-pentane, n-hexane, n-heptane, n-octane, n-nonane, n-decane, and substituted variants of these materials. Representative cycloalkanes include cyclopentane, methylcyclopentane, cyclohexane, methylcyclohexane, ethylcyclopentane, cycloheptane, and others. Finally, representative aromatic hydrocarbon materials which are typically found in crude oil include benzene, toluene, ethylbenzene, p-xylene, m-xylene, o-xylene, naphthalene, and a wide variety of other comparable materials. Little or no C.sub.1 -C.sub.4 compounds are present in most supplies of heavy crude oil. However, the specific chemical composition of crude oil materials will vary based on numerous factors, including the type of oil under consideration and its geographical origin.
As indicated in The Chemistry of Petroleum Hydrocarbons, Ch. 4, pp. 49-62, Benjamin T. Brooks (ed.), Reinhold Publishing Corp., New York (1954), crude oils are typically classified by specific gravity or a gravity scale known as "API" gravity established by the American Petroleum Institute. It is generally presumed that the higher the specific or API gravity of a crude oil composition, the more valuable components (e.g. fuel precursor materials) it contains. In particular, higher specific or API gravity values for a given supply of crude oil generally signify a greater amount of gasoline and kerosene components/precursors in the oil. In contrast, lower specific or API gravity levels will generally represent an increased level of heavier, less desirable components and diminished levels of smaller organic molecules which are important in fuel production. Recent studies have shown that, in the past ten years, the API gravity of crude oil materials from sources in the United States has been decreasing by about 0.17% per year, with the sulfur content increasing by about 0.027% per year. As the API gravity of crude oil supplies has decreased, the need for economically viable cracking/processing methods regarding these materials has correspondingly increased. These processing methods should likewise be capable of treating shale oil, tar sands, and other alternative oil compositions as traditional supplies of crude oil become less abundant.
The need for a highly efficient hydrocarbon cracking method is also important in the specialty chemical industry. For example, many high molecular weight organic compounds (e.g. natural products) may be used as precursors (starting materials) for the production of lower molecular weight specialty chemicals. One of example of such a precursor material is a product known as "squalane" or "shark oil". This material is a natural product derived from the tissues/organs of various shark species, and is a very heavy long chain alkane (e.g. C.sub.30 H.sub.62). The cracking of this material can yield a wide variety of organic compositions ranging from ethylene to heptadecane. Cracking of long chain, high molecular weight alkanes and other compounds can therefore be used to obtain desired reaction products which may be suitable for numerous applications in the specialty chemical industry as noted above.
Regarding the cracking process in general (which is most often discussed with reference to the treatment of petroleum products), many different procedures may be used as discussed in Organic Chemistry, Robert T. Morrison, et al., 3rd ed., p. 110, Allyn and Bacon, Inc., Boston, Mass. (1973). For example, one widely-used cracking method is conventionally known as "thermal cracking". Thermal cracking procedures involve the application of heat to an initial supply of hydrocarbon materials. As a result, alkanes are converted/degraded into alkenes (e.g. ethylene [C.sub.2 H.sub.2 ]) and other compositions in lesser amounts (e.g. hydrogen). In another method known as "hydrocracking", a selected hydrocarbon composition is combined with hydrogen within a preferred temperature range of about 250.degree.-450.degree. C. Hydrocracking specifically involves the dissociation of carbon-carbon bonds in the selected hydrocarbon composition, followed by hydrogenation of the dissociated materials to produce desired reaction products of lower molecular weight. "Steam cracking" typically involves the combination of steam with a selected hydrocarbon, followed by the application of heat (e.g. the maintenance of a temperature level of between about 700.degree.-900.degree. C.) and subsequent cooling.
Finally, a process known as "catalytic cracking" is particularly useful in the production of fuel materials (e.g. gasoline., kerosene, and the like). Catalytic cracking processes were first developed in the 1920s-1930s and typically involve placing the selected hydrocarbon composition in contact with a catalyst material (e.g. acid silicate catalysts including but not limited to silica-alumina-nickel and other comparable catalytic agents) at relatively high temperatures (typically between about 350.degree.-600.degree. C.). From a chemical standpoint, catalytic cracking processes basically involve molecular cleavage of the starting hydrocarbons in association with the transfer and addition of hydrogen atoms using a series of carbonium-ion conversion sequences. The resulting cracked products are highly suitable for use in petroleum fuel processing.
Regarding the production of petroleum-based fuels (which is the primary use for hydrocarbon cracking technology), the cracked product will typically include many different low molecular weight compounds including branched alkenes and alkanes. Numerous conventional procedures may be used to separate and isolate desired fractions from a cracked product having multiple components therein. These processes are known in the hydrocarbon processing art and involve (1) distillation in order to separate desired materials by boiling point; (2) solvent extraction processes in which desired fractions are isolated based on differences in polarity and other physical characteristics; (3) crystallization in which various compositions are separated from each other based on different solubility levels; and (4) chromatography which basically involves the separation of desired fractions using differences in adsorption and charge characteristics. Accordingly, many different methods may be used to separate multiple fractions in a cracked hydrocarbon product, with the present invention not being limited to any particular separation processes. Information regarding separation methods for mixtures of cracked hydrocarbon materials are discussed in The Chemistry of Petroleum Hydrocarbons, Chs. 7-10, pp. 103-274, Benjamin T. Brooks (ed.), Reinhold Publishing Corp., New York (1954) [which is again incorporated herein by reference].
Notwithstanding the cracking methods described above, a need remains for a highly efficient and versatile cracking process which provides the following benefits: (1) applicability to a wide variety of different petroleum and non-petroleum hydrocarbon compositions (e.g. crude oil, refinery waste products, long chain organic molecules of biological origin, and the like); (2) the avoidance of metal catalytic agents and other comparable reagents; (3) the ability to process and crack hydrocarbon materials in the presence of heavy metals and/or sulfur without loss of effectiveness; (4) the absence of large, complex, and energy-intensive processing equipment; (5) the ability to process hydrocarbon materials in a rapid, continuous, and non-labor-intensive manner with a minimal degree of system maintenance; (6) a lack of chemical solvents and the costs/environmental controls associated therewith; and (7) the use of a processing system with a high degree of simplicity and a minimal number of components which facilitates on-site treatment of hydrocarbon materials at remote locations. The present invention provides all of these benefits in a highly unique manner and represents an advance in the art of hydrocarbon cracking as discussed below.